1. Field of the Invention
The present invention pertains to unity gain amplifiers for use with data sampling systems and more particularly to dynamic offset correction of these unity gain amplifiers.
2. Description of the Prior Art
Differential amplifiers exhibit various operating characteristics. One such characteristic is called gain, which is defined as the ratio of the output signal to the input signal of the amplifier. Another characteristic of the differential amplifier is called offset voltage which is defined as the amount of potential difference which must be applied between the two inputs to the differential amplifier in order to make the resultant output voltage zero. The magnitude of the offset voltage of the differential amplifier is not a static number. The magnitude of the offset voltage may change with many parameters, chiefly among these is temperature.
The prior art attempts to correct for offset voltage in differential amplifiers involve the use of large coupling capacitors. Such large capacitors are not amenable to integrated circuits however. Another attempt to provide offset voltage correction is to use a smaller coupling capacitor which is buffered by an operational or differential amplifier. The smaller capacitor can be accommodated in integrated circuits, but the buffer amplifier introduces its own offset voltage which must be further corrected.
In the case of a differential amplifier without a feedback loop, the offset may be corrected readily via the second input to the amplifier. However, in a configuration where a feedback loop is present the second input is used for the feedback and, therefore, unavailable for offset control.